It is well known that the utility of a commercial molding plastic is influenced by its color and clarity. The commercial polycarbonates disclosed in polyester/polycarbonate blends of the prior art are essentially colorless or only slightly yellow with a Gardner b color value less than 5. Essentially all the polyesters based on 1,4-cyclohexanedimethanol described in the prior art, or such as those described specifically in U.S. Pat. No. 2,901,466, are prepared using a catalyst system based on titanium. For example, sodium hydrogen hexabutyl titanate, acetyl triisopropyl titanate, tetraisopropyl titanate, and tetrabutyl titanate are some of the more common catalyst systems used to prepare these polyesters. The commercial polyesters based on 1,4-cyclohexanedimethanol, like the polycarbonates, have excellent clarity and color when prepared with a titanium catalyst. However, the blends of clear, colorless Lexan 101 polycarbonate or Merlon M-40 polycarbonate and clear, colorless Kodar A150 polyester are reddish-orange in color, having a Gardner b color value greater than 20.
The polyesters which are disclosed in the polyester/polycarbonate blend art are described more completely in U.S. Pat. No. 2,901,466. U.S. Pat. No. 2,720,507 discloses the use of organotin compounds useful as polyester polymerization catalysts.
Blends of polyester prepared with tin catalysts and bisphenol A polycarbonate are not believed to be disclosed or suggested in the art. The prior art does not disclose or describe the color of polymer blends prepared using various catalyst systems.
U.S. Pat. No. 4,391,954 discloses blends of bisphenol A polycarbonate and the polyester consisting of units of terephthalic acid, isophthalic acid, and 1,4-cyclohexanedimethanol.
U.S. Pat. No. 4,088,709 discloses blends of bisphenol A polycarbonate and poly(tetramethylene terephthalate) containing a phosphorus stabilizer. U.S. Pat. No. 4,125,572 discloses compatible blends of bisphenol A polycarbonate with polyester and U.S. Pat. No. 4,452,933 discloses a process for stabilizing blends of bisphenol A polycarbonate and polyesters.